PAX-5 encodes for B-cell-specific activator protein (BSAP), a marker for B-cells, including B-lymphoblastic neoplasms and maturation stage. It is found in most cases of mature and precursor B-cell non-Hodgkin's lymphomas/leukemias. In approximately 97% of cases of classic Hodgkin's lymphoma, Reed-Sternberg cells express PAX-5. PAX-5 is not detected in multiple myeloma and solitary plasmacytoma, making it useful for such differentiation. Diffuse large B-cell lymphomas do express PAX-5 save for those with terminal B-cell differentiation. T-cell neoplasms do not stain with anti-PAX-5. There is a strong association with CD20 expression.